Well testing techniques have long been used in petroleum recovery operations for testing characteristics of a selected formation and the fluid in that formation. Well test equipment thus typically includes a ball valve or flapper valve carried downhole on the test string so that the flow path may be selectively opened and closed to allow fluid to pass from the formation, through the casing perforations or open hole, through the valve, and into the test string. According to one technique, the formation fluid may flow through the valve to the surface for sampling, although more recent techniques do not require sufficient formation pressure to force formation fluid to the surface through the valve.
Geologists have long recognized that a significant amount of valuable information regarding formation characteristics can be obtained by analyzing pressure, temperature, flow rates, and composition taken under reservoir conditions in a well bore below a valve which is controllably opened and closed. By selectively modifying the duration of "shut-in" and "flow" periods while monitoring these parameters below the valve, geologists can perform buildup and drawndown analyses under reservoir conditions, thereby providing useful information regarding the anticipated productivity of the formation.
Prior art testing techniques allowed for the storage of data indicative of downhole conditions, so that this data could subsequently be retrieved to the surface with other downhole equipment and then analyzed to determine useful information. Preferred test monitoring techniques today, however, allow for the transmission of downhole data to the surface for analysis during "real time", i.e., data is transmitted from a downhole sensor to the surface almost instantaneously, so that the testing operation itself can be adjusted based upon the information obtained. Real time testing data transmission techniques, for example, thus enable the number and time duration of shut in and flow periods to be adjusted based upon information transmitted and evaluated at the surface during the test and essentially instantaneous with the generation of that information by the downhole sensors.
Certain prior art test equipment monitors pressure and temperature conditions utilizing sensors which are lowered into the well bore on a wireline rather than being run in with the downhole DST tools. This type of DST monitoring technique, such a Halliburton's E-Latch system and Flopetrol's Must system, require that a pressure seal be established between the downhole test equipment and the sensor and related equipment which are lowered into the well bore via the wireline. Effecting a seal between downhole equipment and wireline equipment containing pressure and temperature sensors can be unreliable. A passageway may be provided around the test valve for fluid communication with a mating passageway in the wireline lowered equipment containing the sensors, but the downhole passage must then be closed off to prevent fluid flow around the valve when the wireline equipment and sensors are returned to the surface. Accordingly, equipment of this type has not been widely accepted in the petroleum recovery industry.
Flopetrol's DataLatch system has full bore capability and utilizes test sensors positioned downhole with the test valve and related equipment. This technique is typical, however, of prior art techniques which utilize an electrical "wet connection" between the downhole sensor and the wireline for data transmission. A downhole wet connection is an electrical connection which is ideally kept "dry" by a covering, such as an elastomeric boot, which fits around the physically mated electrical connectors. A wet connection ideally isolates the downhole well fluids from the connector, and hopefully the well fluids thus do not significantly affect the accuracy and reliability of the data signal being transmitted across the connection. In practice, however, this type of connection is not dry and the transmitted data may be significantly affected by the presence and type of well fluid. The reliability of the transmitted data is thus poor, and it is often difficult and time consuming to determine if and when the desired electrical connection has been made due to alignment and connection problems associated with the boot.
The DataLatch system also utilizes a complex technique for mechanically latching the downhole equipment and the wireline lowered equipment. The technique basically requires selective tension or slack manipulation of the wireline for latching the components and operating the system. Such "pull and slack" wireline operations are time consuming and generally considered unreliable. Moreover, wireline manipulation operations which require that tension be maintained on the wireline are difficult or impossible to perform during certain types of petroleum recovery operations, e.g., when working from a floating vessel.
Other well test equipment, such as Flopetrol's Spro system, does not provide full bore testing capability, and thus has the disadvantages previously mentioned with respect to restriction of the flow path for both fluid flow and wireline tools. Moreover, the Spro system has many of the additional disadvantages of Flopetrol's DataLatch system, including the disadvantages associated with the wet connection and with wireline pull and slack manipulations.
The disadvantages of the prior art are overcome by the present invention, and improved methods and apparatus are hereinafter described for reliably transmitting downhole testing information by a conductor wireline to surface manipulation and recordal equipment.